Irunking arrangement



v 1,641,933 p 1927' R. s. RICHARDSON TRUNKING ARRANGEMENT FOR AUTOMATIC TELzruom fs TEm Original Filed 11, 1921 5 Sheets-Sheet l IfifilTiF- Eudu: E. Emhards an Se t. 6, 1927. 1,641,933

R. G. RICHARDSON 'TRUNKING ARRANGEMENT FOR AUTOMATIC TELEPHO NE SYSTEMS led .11. 1921 SSheets-Sheet 2 I Racine E Efizhardsnn 1',64l,9 Y p 1927' .R. G. RICHARDSON 33 TRUNKING ARRANGEMENT FOR AUTOMATIC TELEIHONE SYSTEMS Original Filed 001:. 11, 1921 5 ts-Sheet 3 Imrsnlnr' Each-1E E. Ziwhardsun mi Sept. 6, 1927. ,933

R. G. RICHARDSON TRUNKING ARRANGEMENT FOR AUTOMATIC TELEPHONE SYSTEMS oii inal Filed Oct. 11. 1921 5 Sheets-Sheet 4 Invenlnr' Racine Efiwhardsnn Sept. 1927. 1,5 3

R. e. RICHARDSON TRUNKING ARRANGEMENT FOR AUTOMATIC TELEPHONE SYSTEMS Original Filed Oct. 11, 1921 5 sheets-sheet 5- Patented Sept 6, 1927.

UNITED {STA -Es RODNEY'G. RICHARDSON, or orircnooy nninors, AssIGNoR o AUTOMATIC ELECTRIC I1\TC.,-v or CHICAGO, I nINors, A .CoRronATIon or DELAWARE.

THINK NG ARRANGEMENT non AI T MATI QTELEPHONE SYSTEMS.

Original application fi1ed 0ctober 1 1,

. This'application is a division of application #507,009, filed October 11, 1921, patv ented October 6, 1925, #1,556,307.'

The present invention relates to trunking 5 arrangements for automatic" telephone systems in general, but is concernedmore part cularly with trunking arrangements for such systems as employ non-numerical trunk 'selecting' switchesthat are seized by auto-' j 'matlc selector switchesyand the principal object, briefly stated,is theprovision of new and improved trunking arrangements whereby the trunk selecting movement of a non.

numerical switch in a systemof this type,jor

'15 the maximum number of trunks which such a switch will havelto test is considerablyreduced.

Another object is to provide an improved non-numerical switch us ng a plurality of to find an idle one,

0 relays 'to select an idle trunk insteadoif the improved.

' .iThese objects, together withv others-that" fare not specificallypointed outriow, will be 7 I morefully pointed out hereinafter, reference Q'being had to the accompanying drawings comprising Figures '1-5, inclusive, which show by means of the usual circuit diagrams sufficient of the apparatus employed in a systeni embodying the principles of the invention to enable the same to' be understood. 1

placed together with Fig. l'ove'r Fig. 2 and ic al switches to the major] group ot'iifty trunks shown on the left hand side of the two sheets. 3

Figs. 3 and-4, when arranged in order I with. the corresponding llnes 1n alignment, f represent sufficient of the apparatus'used' 1n the trunking layout shown inFigs l and 2 to enable the same to be understood,

while the trunks outgoing fromthat group are all'in use. p l

A still further object is the provision of new and improved circuit.v arrangements 'whereby the operation of a selector switch is In the. drawings, .Figs. 1 and '2, when 1921, Serial NoL' 507,00 9; Divided and this application filed. June 10, 1925. Serial No. 36,117.

Fig. '5 is a circuit diagram showing a group of non-numerical switches which are difi'erentfrom those shown in Fig. 3. These switches are ota type which may also be used in alayoutsuch'as is shown in Figs. 1

and 2, for convenience it will be assumedthat the system includes both types of switches.

-Referringnow particularly to Figs. '1 and 2, 1 the trunking layout shown therein will be explained more in detail. It hashereto- "fore been thepractice, when "the so called I plunger type of non-numericalswitches are used in' similar layouts, to divide the major group of outgoing' trunks, or the group" 'wlnchfcorresponds-to the group shown on the right hand side of the two drawings, into subgroups of ten trunks each, in accordance 1 with the'nurnber of trunks to which a "plunger type switch has access. Similarly, when' step by step rotary non-numerical switches are used the practice has been to dividethe major group of outgoing trunks intoj sub-groups of twenty-five trunks each,

in accordance with the number of trunks to" I whicha switch of this type has'access. This practice, so far as is known,'-has, been'fol- 1 lowed invariably, regardless of the number ent .c'ase,' liojwever," the major group of outgoing trunks is preferably divided into ten subgroups, corresponding to thej'number of oftrunks in ,the'major group. In the presoutgoing trunks inthe majorgroup' and conseqiiently there are three outgoing trunks in each subgroup. If the ma or group comprised forty out-going trunks ,then each sub-- groupwould: comprise four trunks, or if the maj'or.group'comprised only twenty trunks 1 then each sub-group would comprise only two trunks. It willbe seen now thatas long as" the maj or group of outgoing trunks :is leg j han' there will not be as manycas ten trunks persub-group, which heretofore has"been the minimum number, and wlth major groups of a number much less than 100 the numbertot trunks in each subgroup g ou s of trunks have a correspondingly in order to find an idle one.

is correspondingly less andconsequently the; it switches which have 5 access 'to. these sub 108 It will 'be'seen from an examination of the drawings that there isa trunk line extending from each selector group on the left to a non-numerical switch in each sub group on the right. In the first group of selector trunks, the group in the upper left hand corner of Fig. 1, the first trunk leads to a non numerical switch in the first sub group, or the sub group in the upper right hand corner of Fig. 1. The second trunk in this selector group leads to a switch in the second sub group, the third trunlr to a switch in the third sub group and so on The trunks I from the second group of selectors extend to switches in the several sub groups in the same manner as those from the first selector group, except that a slip is introduced and trunk No. 1 in the secondselector group leads to a switch in the third sub group, the second trunk to a switch in the fo'urth sub group, and so on down to the last trunk 1n this group Which leads to a switch in the second sub group. It will be observed that thissame slip is carried out all along down the line. This slip distributes the tra-fiic evenly amongst the various sub groups.

This revision of the trunking arrangement, in decreasing the number of trunks-1n each sub group, not only decreases the time required for an idle trunk to be selected, but

, when relay switches are used effects a great saving in equipment for the reason that the number of relays insuch a switch 1s proportionate to the number of trunks to which the switch has access. i

Referring now particularly to Flg. 3, the

1 selector D shown therein is mechanically of the usual vertical and rotary type and accordingly has its bank contacts arranged 1 11 horizontal rows or levels. This switch 1s operated according to the well known twowire system of control. The circuits of this 7 switch are showncomplete and will be described tully hereinafter.

The non-numerical switch E which is accessible to the selector D, does not have the usual mechanical trunk selecting movement but has instead a plurality of relays which operate one after the other to select an idle trunk. The circuits of this switch also are shown complete and will be described iully hereinafter.

Each of the trunks to which the switch E, together with the other switches in the same group, has access, is assumed to extend to a repeater, such as the repeaters F, F, and F Figure 4:, and thence by way of a two con- 'ductor trunk line such as the trunk lines X,

X, and X to another oifice in the system. These repeaters F, F, and F are all identi cal with each other and, with the exception of an added relay, are identical with the tWo wire repeaters that are now in common use.

The relay group KG shown in thelower part of Fig. 4. is used for the purpose of making all the trunks incoming to the group busy as soon as all the outgoing trunks are taken for use, or rather, as soon as the last call arrives at the group. This operation will be explained more fully hereinafter.

Of the switches H, H, 11 H", and H", Fig. 2, and of which only H, H and H are shown in the detailed circuit drawing in Fig. Leach is similar to theswitch E Fig. 3, in that no mechanical step by step arrangement is employed to pick out an idle trunk line, but are different in that the trunks are preselected as will be eXplained more fully hereinafter.

The apparatus having been described more or less in general will now be describedin connection with a detailed description of its operation, For this purpose, it will be assumed that a call comes through the exchange by way of the selector D, Fig. 3, The selector D, it may be pointed out, is one of the selectors which has access to the second groupof trunk lines on the left of Fig. 2, counting from the bottom. We shall assume further that when the call comes in none of the switches E Efi inclusive, 2, are in use and consequently all of thetrunks outgoing from that sub group are idleat this time. lVhen the call comes in as assumed, the selector D is seized at the bank contacts 2, 3, and 4, or their multiples, in-which the trunk line comprising conductors 5, 6, and 7 terminates and line relay 10 is energized over the calling subscribers loop in: series with the impulse springs of the calling subscribers calling device. Upon energizing, line relay 10 circuit for the switchin relay of the switch.

which seized the selector 1).

The calling subscriber now manipulates his calling device in accordance with the next digit in the desired number, thereby producing a corresponding number ofinterruptions in the circuit of line relay 10. As soon as line relay10 falls baclr'in response to the first interruption produced in-its circuit, it closes at armature 15 the circuit of the slow acting relay 12. The slow acting relay 12, upon energizing, prepares the circuit of stepping relay 13 at armature 22 and at armature 21 opens a. point inthe circuit of rotary magnet 23 and closes a point in the circuit of Vertical magnet 20. Each time line relay 1O energizes at the end of an in circuit of rotary magnet 23.

' being slow acting, are both maintained energized throughoutthe series of interruptions. By the operation of the vertical magnet, Which energizes each time its circuit is closed following an interruption in the circuit of the line relay 10, the switch shaft and wipers are raised step by step until tlie'latter come to rest opposite the desired level of contacts, which. will be assumed to be the level in which the trunk line comprising conductors thereby completing a circuit for stepping T relay 13. Stepping relay 13, upon energizing, closes a locking circuit for itself at armature 25 in series with interrupter contacts 27, andat armature 24 prepares a circuit tor rotary magnet 23. After the last interruption is produced in the circuit of line relay 10, armature comes to rest against its working contact thus leaving the circuit of slow acting relay 12 open. Upon deenergizing, relay 12 opens the initial circuit of stepping relay 13 at armature 22 and at armature 21 opens the circuit of vertical magnet and closes the circuit of rotary magnet 23. Rotary magnet 23, upon energizing, advances the Wipers 3234-,'1nclu SIVG into engagement with the first set of contacts in the level opposite which they are relay 13. Stepping relay 13, upon deenei"-,

gizing,opens another point in armature andat arn'iature 2 iopens the net'23 now die-energizes and closes the inter rupte'r contacts Qi'again. i

"From lilllS point, the operation depends upon whether the trunk line which terini- 'nates in the first set of contacts' is busy or idle. if it is busy, test wiper is in en-' gage-nicnt with a gi'ouudcdcoutact and stepping relay 13 energizes again over a circuit .which includes wiper 33 and armature 29 and its resting contact.

Upon energizing, stepping relay 13 closes-the previously described locking circuit for itself at armature and at arn'iature close rotary magnet 23. .Rotary magnet 23, upon energizing, steps the wipers into en a ement with the next set of contacts and again opens its nterrupter contacts 27. This alternate operation of the rotary magnet and the trunk line terminating in bank contacts 35'-37, inclusive, which is the first set of contacts in the level, is idle, when the call is made as described. 3 This being, the case,

there is no direct circuit closed for stepping its circuit at Rotary inag to, te etc.

the circuit of l ner-clay [i l to battery.

atel ener izes over the followin )ath:

it! D From groir tact of u in d by way of theworliing' conure l6 and the said armature, 'tchin ieray rhinterrupter contacts 27, normal contacts 26, and stepping relay to battery. Stepping relay 13,- however, ie ing wound with comparatively tew turns is not able to energize over this circuit on acconntot the hi 'h resistance of switching Shi'ite relay 1d, upon enerdisconnects test wiper 33 from a n its own winding and that of v '33 and connects it to the reductor 6 at armature 29; re

in the armature o't line'renature 30; and at arinatures 28 conr is the trunk conductors 5 i the upper and lower windings l0 and extends them by Way 1g contacts of the said armaand'Se, bank contacts conijluctors 38 and 40, armaand their resting cont-acts line relay of switch E ctive ly. "Line relay 50, aces ground upon release i at armature 57, thereby i. holding circuitfor the ser ing soon as ground is placed on release trunk 3.9 by the pulling up of switching is niade busy immediately to the other switches having access to it. In this case,

hes-is made busy through the coinuctor 9O to which all the release "more are normally connected ing contacts of armature 60, is seen now thatyany other call which comes in atthis stage will not z to a rush leading to the group in which is located but will be diverted grcup. I

To continue with the operation ofthe' switch E line relay 50, upon energizing, in addition to placingground on release trunk conductor 39 as described, closes at armature 5 the following circuit: from ground by way of armature 56 and its work ng contact, switching relay 51, armature 69 and its resting'contact, arniature- Hand its resting contact, and thelower winding or v This circuit, it will be noted, includes relay 51 and thelower Winding of the relay Satin series. -As a further result of the operation of the line-relay 50, armature is connected to a pointbetween the 'Windii'igof relay 51 and the lowe':

switches back of it before p p release relay 11 has had time to deenergize. It will be noted 'that'as A of the switch D, the seized trunk winding of relay Armature is normally connected to ground through the resting contact of armature 59 and said armature, armature 63 and its resting contact, armature 67 and its resting contact, and armature 72 and its resting contact. Switching relay 51 is accordingly short circuited and prevented from energizing. Relay 54, however, energizes; closes a. locking circuit for itself at armature 73; disconnects ground from the point between its lower winding and that oi. switching relay 51 at armature 72 and connects up release trunl; conductor 77 instead; disconnects its own lower winding and connects up the lower winding of relay 53 at armature 741; and at armatures 71 and 7 5 connects up the upper and lower series of contacts and armatures to trunk conductors 76 and 78.

From this point the operation depends upon whether the trunk line comprising conductors 76-78, inclusive, is busy or idle. If it is busy release trunk conductor 77 is grounded and switching relay 51 is still short circuited. With this condition existing relay 53 energizes; closes a locking circuit for its own upper winding and opens the locking circuit of switching relay 5st at armature 68; connects the point between its own lower winding and the winding of switching relay 51 to release trunk conductor 80 at armature 67; disconnects its own lower winding and connects up the lower winding of relay 52 at armature 69; and at armatures 66 and 70 disconnects the trunk conductors 76 and 78 and connects up the trunk conductors 79 and 81. Relay 54 deenergizes now in response to the opening of its locking circuit but does not perform any particular function at this time. If the trunk line comprisingconductors 79S1, inclusive, is busy at this time there is a ground potential on re lease trunk conductor 80 and relay 52 by action identical with that of relay 53 justdescribed, transfers the connection to the trunk line comprising conductors 82-84, inclusive, and relay 53 deenergizes.

In the present case, however, we shall as sume, as before stated, that the trunk line comprising conductors 76-78, inclusive, is idle at thistime and consequently there is no ground potential on release trunk conductor 77, and as soon as relay 5 1 has energized and transferred the circuits in the manner described, switching'relay 51 ener- Y gizes in series with the lower winding of relay Relay however, does not energize in series wlth the switching relay 51 on .account of the high resistance of the said switching relay 51. Switching relay 51, upon energizing, disconnects release trunk conductor 77 t own winding and the lower winding of relay 53 armature 59 and connects it to ground through the working contact of armature iroin the point between its 56 and said armature, thus causing the seized.

trunk to test busy immediately to the other switches having access to it; disconnects release trunl: conductor 39 from the common conductor 90 at armature 60 and connects it by way of the previously traced series of armatures and contacts to release trunk conductor 77 5 and at arinatures and 61 disconnects trunh conductors 38 and 410from the winding of relay 50 and ground, respectively, and extends them by way of armatures 62 and and their resting contacts, armatures 66 and and their resting contacts, armatures 71 and and their working contacts, trunl: conductors 76 and 78, and the normally closed contacts controlled by armatures 110 and 111 to the upper and lower windings of the double wound line relay 102 of repeater F. Linerelay 102 now energizes over the calling subscribers loop and at arn'iature 113 opens a point in the circuit of slow acting relay 103 and closes a circuit for relays 10-1- and 105 in multiple. Relay 105, upon energizing, among other things which will be pointed out more fully hereinafter, disconnects relay 104 from the working contact of armature 113 and substitutes a circuit through armature 120 and its working contact. Relay 10%, upon energizing, places ground upon release trunk conductor 77 at armature 117. This occurs before the slow acting line relay of the switch E has had time to deenergize and maintains a holding circuit for the switch E and other switches behind it.

Returning now to the repeater F, as a further result of the energization of relay 10 1, it closes at armature 119 a circuit for the lower winding of electropolarized relay 106. This winding alone, however, consisting or" a small number of turns of a relatively high resistance, is not able to effectively energize the relay. As a still further result of the energization of relay 10 1 it prepares a circuit for slow acting relay 103 at armature 118, and at armature 116 completes a bridge across the conductors of the trunk line X as fOll0\ s: From the lower conductor of trunk line X by way of the working contact of armature 11 1 and said armature, right hand winding of impedance 107, normally closed contacts controlled by armature 112, upper wii of elcctropolarized relay 106. resting contact of armature 115 and said armature, and the working contact of armature 116 and said armature to the upper conductor of trunk line X. In response to the closure of this bridge, the line relay 01 the automatic switch on the other end of the trunk line X is energized and the switch is prepared for operation in the usual manner. Current is now flowing through both the upper and lower windings of electropolarized relay 106 but the said relay is not energized at this time because the current flowing in either winding is opposite I indirection to that flowing in the other.

The calling subscriber now manipulates his calllng device in accordance with the next digit in the desired number, thereby producing a corresponding number of interruptions n the circuit of line relay 102. Each time line relay 102 deenergizes 111 response to one of these interrupt-ions it opens the circuit of the line relay of the automatic switch on the distant end of the trunk line atarmature 114, thereby causing the said switch to operate in the usual manner. Slow acting relay 103 is maintained energized through-' .out the series of interruptions over a circuit which includes armature 113 audits resting contactand armature118and its working contact. Upon energizing, slow acting relay 103 completes the bridge across the conductors otthe trunk line 'X by a more direct path, which excludes the right hand winding of impedance 107 and the upper winding of electropolarizedrelay 106 at armature 115 and its working contact. This is the usual expedient made use of in order to obtain connection is finally completed and the called subscriber has been signalled and has responded by removing his receiver, the current flow in the trunk line X and conse quently in the bridge across the conductors of the said line in the repeater F is reversed by the final switch in the distant exchange. when this occurs, thetwo windings ofelectropolarized relay 106 which heretofore have opposed each other now asslst each other in-energ1zing the relay. Upon enerture'124; places a shunt around armature 114 and itsv working contact at armature 1 25; and at armature 126 closes the c1rcu1t of reversing relay 101; Upon energizing, re-

relay 101 shifts the bridge across the trunkline X so as to include both windings of impedance 107 at armature 112, and at armatures 110 and 111 reverses the incoming versing v trunk conductors '76 and 78 as regards their in this manner connection with the upper and lower windings meters, coin boxes and the like but does not have'anything in particular to, do with the present invention, the circuits being shown because of the fact that 11s I e moreor less a standard arrangement.

relay 106. places a shunt around armature 115 and its resting contact at armaof line relay 102. Thisfreversal of current flowis usedin some cases to operate 7 calling and called subscribers may now converse with each other as desired, the talking circuits that are shown being outlined by heavy conductors.

When the conversation is completed the calling'and called subscribers replace their receivers. When the receiver is replaced at the called substation the current flow in the conductors of the trunk line X is reversed back to normal whereupon electropolarized relay 106 retracts itsarmatures and upon so doing removes the shunt from around arma ture 115 and its resting contact at armature 1 24; removes the shunt from around arma-' ture 114 and its working contact at armature 125; and atarmature 126 opens the circuit of reversing relay 101. Reversing relay 101, upon deenergizing, reverses the current flow in the calling .subscribers loop back to normal. This operation, however, does not perform any useful function in the present case.

l Vlien the receiver is replaced at the call-- ing substation the circuit or line relay 102 of repeater F is opened and the said relay,

upon deenergizing, opens the'bridge across the conductors of the trunk line X at armature 114,1 whereupon, the. switches in" the distant exchange vrestore tl11emselves"to normal, position in the usual manner. Asa further result ofthe deenergization of line relay 102, it opens the circuit ofslow acting release relay 105 and closes the circuit of slow acting relay 103 at arma ture 115. Release relay 105, upon deenerautomatic gizing, opens the circuit of relay 104 at armature 120. Relay 104, upon deenergizng, opens the circuit of slow acting relay 103 at armature 118 and at armature 117 removes ground from release trunk conduc' tor 77 When ground is removed from release trunk conductor '77, relay 54' and switching relay 51 of the switch E and switching relay 14 of the selector D, together with the switching relays of the various other tion before the selector D wasr'eached, dee energize. The deenergization of the two relays mentioned in the switch E restores that switch to normal condition andconnectsfup release trunk-conductor 39 to common conductor'90 at armature 60.

In the selector D, switching relay 14, upon deenergizing, completes a circuit for release magnet 19'as follows; from ground by way of resting contact ofarmature 30 and said armature, armature 15 and its .resting con- "tact, armature '17 and its resting contact,

o fi-normal contacts 18, and release magnet 19 toba-ttery. By the operation of the release D are restored "to normal, position in the usual manner, the circuit of release magnet 19 being opened at oifnormal contacts 18 by the switch shaft when it reaches normal 125 "magnet, the shaft and wipers of the selector i switchesfwhichwere engaged in the connecposition. The other switches engaged in the connection before the selector D was reached are restored to normal position in the usual The entire connection is now released and the apparatus is now ready for another call.

Referring now again to Figs. 3 and A, the function of the relay group RG, Figure 4, together with its associated equipment will now be explained in detail. We shall assume that the group of trunks, to which the switch E and others has access, is idle and that a call comes in over one of the switches, the switch E for example. As soon as the trunk line comprising conductors 38, 39 and 40 leading to the switch E is seized by a selector such as the selector D, a ground potential is thrown upon release trunk conductor 39 by the selector in order to make the seized trunk busy immediately. This ground potential, as hereinbefore pointed out, extends by way of the common conductor to the release trunks of all the switches, in that group. This ground potential extends also by way of conductor 90 to relay 130 of the relay group RG, Fig. 4. Relay 130, upon energizing, connects the common conductor 90 with conductor 142 at armature 134. This operation, however, does not perform any particular function at this time. As soon as the various relays of the switch E have had time to function, release trunk conductor 39 is disconnected from common conductor 90 at armature .60 of switching relay 51, whereupon relay 130 of relay group RG deenergizes and disconnects the common conductorSO from conductor-14:2. As a further result of the energization of switching relay 51 of the switch E the trunk line extending to the repeater F is seized and the repeater is made ready for operation in a manner hereinbefore explained. As soon as relay 105 ofi'epeater F, is energized, the first one of a chain of contacts in the circuit of relay 132 of relay group RG is closed at armature 121, and at armature 122 the resistance 123 is disconnected from conductor 139 and ground'is placed on the latter, thereby closing a circuit for relay 131 of relay group RG by way of armatures 138 and 137. A circuit is closed at this time for relay 133 of relay group RG as follows: from ground by way of conductor 139, armatures 122 and 122 in multiple and their resting contacts,

resistances 123 and 123 conductor 141, and relay 133 to battery. Relays 131 and 133 energize simultaneously and the latter, upon energizing, opens the circuit of the former at armature 138, whereupon, the said relay 131 deenergizes. It is seen now that with one of the repeaters of the group comprising repeaters F, F and F busy, ground is placed on conductor139 to close the circuit of relay 131 but relay 133 is energized and has the circuit of the former relay open.

We shall assume that another call comes in and that one of the non-numerical switches in the group in which the switch E is located seizes one of the remaining r epeaters, the repeater F 2 for example. As soon as the non-numerical switch is seized, ground is placed on the common conductor 90 in a manner described before but does not produce any result in the relay group RG other than merely operating relay 130. As soon as the non-numerical switch has had time to function and seize the repeater F ground is removed from the common conductor and relay 130 deenergizes. Relay 105 of the repeater F upon energizing, closesanother point in the circuit of relay 132 at armature 121 removes the resistance 123 from the circuit of relay 133 and places a multiple ground on conductor 139' at armature 122 Relay 133, which is 111211- ginally adjusted, deenergizes' at this time since its circuit is closed through only the resistance 123 and completes the circuit of relay 131 at armature 138. Relay 131, upon energizing, places ground on conductor 142 at armature 135. This is done in preparation so as to place ground on the common conductor 90 at relay 130 as soon as the sole remaining outlet from this group is taken for use.

Assuming now that another non-numerical switch in this group is seized, ground is thrown upon common conductor 90 in the usual manner, whereupon relay 130 of the relay group RG energizes and connects the common conductor 90 with conductor 1 12 which is grounded at armature 135 of relay 131. As soon as the non-numeri *al switch has functioned, its release trunk is disconnected from the common conductor 90 and the repeater F is seized in the usual manner. All the outlets from this group of switches are in use and if another call were permitted to come into this group at this time it would be lost for the lack of an outlet. No call can come into this group at this time, however, for the reason that the common conductor 90 is maintained grounded by relay 130 of relay group RG and, consequent ly, the calls are shifted to such other groups of non-numerical switches as have idle trunks leading out from them. As soon as relay 105' of the repeater F has energized in response to seizure of this repeater, it completely opens the circuit of relay 133 at armature 122". This, however, does not produce any effect in the relay group RG as relay 133 is already deenergized. As a further result of the deenergization of rela 105 it completes the circuit of relay 132 at armature 121. Relay 132, upon energizing. opens the circuit of relay 131 at armature 137 and at armature 136 places a multi ale ground on conductor 142 and consequently on common conductor 90. Relay 131, upon from groundat" armature 135 but the said conductor is still groundedat armature 136.

W e shall assume for the sake of'illust'rati'on'that the subscriber who is using the switch E and the repeater ll finishes his conversation and replaces his receiver. With theassumption as noted, the connection is released in a manner hereinbefore described and-release trunk conductor 3901' the switch E is connected to the common conductor again. As soon as relayof repeater Fdeenergizes, a-circuit is closed for relay 133 or the relay group in series with resistance 123 but owing to ltS marginal adjustment, relay 133 is not energized at this time. As a further result of the deenergization of relay 105, it opens the circuit of re lay 132 at armature 121. Relay 132, upon deenergizing, removes ground"from conductor 142 and consequently tromthe com- 'mon conductor 90 at armature 136 and at armature 137 closes the circuit of relay 131. Relay S130 and 131 are so adjusted thatthe armature of relay 130l'alls back slightly quicker than the armature of relay 131 is attracted and consequently relay 130 deenergizes" at this time and disconnects, the

common conductor 90 from conductor142 at armature 134 before relay 131 has had tiineto energize; The circuit conditions of the relay group ltGare now, the same as theywere just before, the repeater F was seized, that is, conductor 142 grounded and the circuits are in readiness for placing ground on the common conductor90 as soon as the last outlet troin this group is taken for use- If we assume now that one of the repeaters F or F the repeater F for example becomes idle,,thus giving more than one available outlet from this group, before another call comes in to this group, the circuit of relay 131 isopened and ground is removed from conductor 142 aswill now be pointed out. Relay 105 upon deenergizing, opens at armature 121 'st1ll another point 1n the circuit of relay 132 at armature 121 and at armature 122 *placesresistance 123 in multiple with resistance 123 whereupon, the marginally adjusted relay 133 energizes and opens the circuit of'relay 131 at armature Relay 131 now deenergizes and re moves ground from conductor 142 at armature 135. I

conductor 90, which has the rel-ease trunk conductors of. all the idle inlets connected with it,'is connected with the conductor 142 of the relay group RG, and it there is only one remaining outlet from thegroup there is a ground potential on conductor 1 1-2. and

relay 130will become locked. Consequently, when the switch cuts through and the last outlet is taken for use, con'ductor.90 is not cleared but .remains connected with the grounded conductor 142 thereby busying all the inlets into this group. It is seen further that the seizure of the last outlet is accompanied by a transfer of theground connection on conductor 142 so as to permit the unlocking of relay 130 as soon'as an outlet again becomes available. The advantage ofthearrangement described lies in the fact that when there is only one available outlet from a group, the hu'syingotthein lets to such group will occur simultaneously with the seizure of the next switch, and all possibility of a call being extended to sec,- ondary switch having no idle outletsis eli1n1- nated.

It is to be understood that this same arthe repeaters associated therewitlnwill have their make busy contacts connected in the same. manner as those or the intermediate repeater F and these other repeatersmay be inserted between either therepeaters; E

and F or the r epeat-er's E and Ft It will be convenient to explain at this time that the switch Ei Figure 3,,may be given access touas many outgoing trunks. as desired by adding more trunk selecting re -L lays and that, without addinganv relays or' other equipment, an additional trunk-can be connected to the resting contacts of arm.- tures 71, 72, a-nd of relay 54. In that case,v of course, the ground which 'is shown connected to the resting contacts oiarma ture 72 is removed. VVith-this extra trunk, if there is no ground onthe resting contact'of armature 72 of relay, 54 when the switchE is seizechit being assumed of course that the trunk in question is, idle, then the energization of line relay 50 is followed immediately by the energization of switching relay 51. which switches the connection through to the normally connected trunk line. In case still more trunks are desired they can be had as before stateth'by adding one relay per trunk together with its associated armatures and contacts.v Each of these added relays may have a spring assembly identical with thatot relay 53 and may be inserted either between r-elavs52 and 53 or between relays 53 andv54. This increase in trunk capacity may be carried out asifa'r as is desired, or until the cost of the switch equals or surpasses the cost of a switch having a mechanical step by step trunk selecting movement. i v

It will be stated. at this point that switches similar to theswitch E Fig. 3Lare assumed to be used in the ventire layout shown in Figs. 1 and 2 the group comprising switches H 1 inwith the exception of elusive, which are of different type. This assumption however is made solely for convenience and to avoid the necessity of duplieating the layout, it being understood that in practice switches of one type or the other will ordinarily be used exclusively in any given situation.

Referring now particularly to Fig. 5, which is a circuit drawing of the switches H, H, and H of the group comprising switches HH*, inclusive, Fig, 2, the switches H and H are omitted, their circuits being identical with the circu ts of switch H. For the purpose of illi ation it will be assumed that allvthe switches in the group comprising switches I'LH, inclusive are idle at this time and that the switch H is seized from one of the selectors which has access to the trunk line comprising conductors 201 203, inclusive. lVith the assumption as noted, a ground potential is placed upon the release trunk conductor 202 immediately by the selector so as to malre the seized trunk busy to the other switches having access to it. This ground potential e2:- tends by way of armature 215 and its resting contact, armature 223 and its rest ng contact, and armature 225 and its resting contact, to common conductor 292 to whiclrall the release trunk conductors of the incoming trunks are normally connected. This makes all the incoming trunks associated with this group temporarily busy and prevents two calls from being received in this group simultaneously, the other calls being shifted to other groups. This ground potential extends also through armat-ure 218 and 1ts resting contact, armature 22 i and its rest ng contact, and armature 226 and its resting contact to conductor 29% to which the trunk selecting relays 210, 21.1, and 212 are normally connected. Similarly this ground potential extends by way of a similar series of armatures and contacts in the switch H to conductor 295 to which all the relays of this switch are normally connected. lIhe same thing is true for each of the other switches in the group. The other terminal of the relays 212, 2 16, and 24:9 are normally connected to common conductor 289, and relay 211 together with the similarly located relays in the other switches is connected to the common'conductor 287. Neither common conductor 28'? nor common conductor 289 has a battery potential on it at this time and consequently none of the relays mentioned energize. Common conductor 285, to which relay 210 and the similarly located relays in the other switches are norm y connected, is connected to battery at this time through the resting contact of armature 221 and said armature, resting contact of armature 232 and said armature, similar contacts and armatures on the switches H and H and the resting contact of armature 252 and said armature. That being the case, the first relay in each switch in this group starts to energize as soon as ground is placed upon release trunk conductor 202 as previously described. Relay 210, upon energizing, disconnects release trunk conductor 202 from common conductor 292 at armature 216, thereby making the remaining switches in this group accessible and allowing all the other relays that started to pull up, responsive to the placing of a ground potential on conductor 292, to fall back. As a further result of the energization of relay 210 it locks itself to release trunk conductor 202 and disconnects itself from conductor 29% at armature 219; locks itself to battery and disconnects itself from common conductor 285 at armature 220; places ground on conductor 290 at armature 217 disconnects release trunk conductor 202 from conductor 291 at armature 218; removes battery from conductor 285 and places it upon conductor 28.6 at armature 221; connects release trunk conductor 202 with'release trunk conductor 276 of the seized trunk at armature 216; and at armatures 215 and 222 connects conductors 201 and 203 with conductors 275 and 277 of the seized trunk. The line and release relays of the automatic repeater to which the trunk line comprising conductors 275-277, inclusive, extends, immediately energize and prepare the switch for operation in the usual manner, and the latter, upon energizing, places ground upon release trunk conductor 276 thereby establishing the usual holding circuit.

The calling subscriber may now go ahead and dial the remaining digit of the desired number in the usual manner.

If we assume that another call comes in this time and that the switch H is the one seized, a ground potential is sent forward over the release trunk conductor 205, through the series of contacts shown, to common conductor 292 and thence to the release conductors of all the idle switches in this group. The battery potential which was placed on conductor 286 by the energization of relay 210 as explained now extends by way of armature 255 and its resting contact, similar armatures and contacts in switches H and H armature 239 and its resting contact, and armature 264 and its resting contact to conductor 287. accordingly relay 24:5 and the corresponding relays in the switches 1 1 11 inclusive start to energize as soon as the ground potential is thrown upon release trunk conductor 205. There is no battery potential on common conductors 285 and 289, however, and consequently the associated relays do not energize. Relay 245, upon energizing, disconnects release trunk conductor 205 from common conductor 292 at armature 234 whereupon, all the other relays which started to energize at this time deenergize and the remaining idle switches are made accessible again. As a further'result of the energizationof relay 245 it locks itself to release trunk conduct-or 205 anddisconnects itself from conduct-or 295 at armature 237; locks itself to battery and discon- 'nects itself from conductor 287 at armature 238; extends the ground potential whichis on conductor 290to conductor 291 at armature235; disconnects release trunk conductor 205 from conductor 295 at armature 236;

disconnects battery from conductor 287 and extendsit. to conductor 288 at armature 239; connects release trunk conductor 205 with seized trunk- The line and release relaysof the switch to which the trunk line compris- 1 ing conductors 278'280, inclusive, extends now energize in the usual manner and the 4 latter places ground on release trunk conductor 279,. thereby establishing the usual holding circuit.

' Assumlng now that another callcomes in to this group and that it takes the switch H the ground potential which is placed upon release trunk conductor 208 is extended forward to common conductor 292 and thence to the release trunk conductors of the switches in this group which are idle at'this time.

The batterypotential which was placed upon conductor 288 by the energization ofrelay 245 ofthe switch H extendsby way of armature 262 and itsresting contact, corresponding armatures and contacts in the switches 11 and H armature 243 and its resting contact, and armature 227 and .its

resting contact to conductor 289. As a result relay 249 and the corresponding relays in switches H and H commence to energize as soon as the ground potential is placed upon release trunk conductor 208. In this case there is no battery potential upon conductors 285 and 287 and consequently neither relay 247 nor 248 of the switch H nor the corresponding relays. in the other switches in this group which are idle at this time can energize. Relay249, upon energizing, removes the ground potential from commonconductor 292 at armature 257, whereupomthe corresponding relays in the switches 1H and H Fig. 2, fall back. As a further result of the energization of relay -249--it locks itself to release trunk conductor 208 and disconnects itself from'conductor 295, at. armature 260; locks itself to battery and disconnects itself from conductor 289 at armature 261; extends the ground potential which is on conductor 291 to common conductor 292'at armature 258; disconnects release trunk'conductor 208 from conductor 295 at armature 259; disconnects battery from'conductor 289 'at armature262, connects release trunk contrunk, line first choice.

ductor 208. with release trunk conductor 282 "of the seizedtrunk'at armature 257; and at armatures 256 and 263 connects up conductors 207 and 209 with conductors 281 and 283, respectively, of the trunk line comprising conductors 281283, inclusive. The'line and release relays of the switch to which the seized trunk extends now energize in the usual manner and'the latter places ground on release trunk conductor 282 thereby establishing the usual holding circuit.

All the outlets from. this sub group of switches are nowin use and if a call were permitted to come into this group at this time it would be'lost for the lackof an out-let. Calls are prevented from coming into this group at this time by the ground potential which is extended forward by way of conductors 290 and 291 to common conductor 292 to which the release trunk conductors of the .idleswitches H and H- are connected.

making the idle switches in this group available again. On the other handif we consider that the switch H becomes idle while the switch H is yet busy the battery potential will be replaced on common conductor making the second trunk line in the group available.

- It will be noted that these switches H-H ,inclusive, always take the first trunk when it is idle, taking the second trunk only when the firsttrunk is busy and the third only when the second trunk is busy. This,

wvhile not 'obiectionable perhaps from a theoretic standpoint, is sometimes undesirable from a practical standpoint owing to the fact that all the trunk lines are not used alike and the switches associated with the trunks which are used the most are subject-- ed to the most wear and may have to be replaced often while the others are practically unused except during the peak of the load which occurs periodically. difliculty can be obviated. if desired, in a -manner' which will now be pointed out.

Working contacts may be placed on armatures 227. 243, correspondlng armatures on switches H and H and armature 262 to This seeming 287 insteadof on common conductor 285 thus which a common conductor may be wired.

This common conductor may be extended to armature 252 of relay 247. 'Thismakes the battery transfer circuit a complete loop. With this loop wired as described the battery connection may be removed from armature 252 and placed on either armature 255.

or armature262. thus making the associated Any suitable method or means for shifting the battery potential by adding one relay to each switch together with the proper contacts and associated conductors. These relays may be inserted between the row comprising relays 211, 245, etc. and the row comprising .relays .212, 246, etc., or between the first named row and the row comprising relays 210, 24.4, etc. It is to be understood also that more switches may be added in a group and that each added switch will be similar to the switch H and may be inserted anywhere along the line between the switches H and While the explanation might be still further amplified it is thought that the foregoing is sufficient to enable the invention to be thoroughly understood by those who are skilled in the art and to whom this specification is directed.

The various features of the invention having been thus described and ascertained will now be pointed out in the appended claims.

What is claimed is".

1. In telephone system, a trunking section comprising incoming and outgoing trunks, each trunk having two line COIlClllC'. tors and a release trunk conductor, a switching device for each incoming trunk comprising a relay for each outgoing trunk, and a circuit completed over the release trunk conductor of an incoming trunk when such trunk is taken for use for energizing the particular relay of the associated switching device which corresponds to an idle outgoing trunk.

2. In a telephone system, a trunking section comprising incoming and outgoing trunks, each trunk having two line conductors and a. release trunk conductor, a switching device for each incoming trunk comprising a relay for each outgoing trunk, a circuit completed over the release -trunk conductor of an incoming trunk when such trunk is taken for use for energizing the particular relay of the associated switching device which corresponds to an idle trunk, said circuit including parallel branches through the corresponding relays in all the other idle switching devices, and contacts controlled by the energized relay for opening said parallel branches.

3. In a telephone system, a trunking section comprising incoming and outgoing trunks, each trunk having two line conductors and a release trunk conductor, means for connecting incoming trunk lines with outgoing trunk lines, said means compristrunk lines multiplied by the number of outgoing trunk lines, means for energizing said relay-s over the release trunk conductors of incoming trunk lines, and means for maintaining said relays energized over the release trunk conductors of outgoing trunk lines.

4,. In a telephone system, incoming and outgoing trunk lines each having two line conductors and a release trunk conductor, a relay normally connected to the release trunk conductor of the incoming trunk line, means for temporarily grounding the release trunk conductor of the incoming trunk line when it is taken for use, the relay being energized to connect the two trunk lines, and means for grounding the release trunk conductor of the outgoing trunk to maintain said relay energized.

'5, In a telephone system, incoming trunk lines, outgoing trunk lines extending at right angles thereto, relays at the points of intersection whereby any incoming trunk may be connected with any outgoing trunk, and local series circuits extending through rows of relays parallel to the direction of the incoming and outgoing trunks, respectively, for controlling the selection of an idle outgoing trunk.

6. In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a line relay, a switching relay for disconnecting the line relay, and circuits for said magnets controlled directly and jointly by said relays.

7. In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a line relay for the switch having a pair of contacts, a switching relay for disconnecting the line relay and also having a pair of contacts. and a circuit for both said magnets including both pairs of contacts in series. 1

8. In a telephone system, a selector switch having directive primary and automatic secondary movements. primary and secondary motor magnets, a line relay having a pair of contacts'closed when the relay is energized, a normally open circuit for the primary magnet passing through said contacts, means for momentarily deenergizing the line relay 'a'plurality of times, a slow acting relay maintained energized by the line relav during a series of deenergizations thereof, and contacts on said slow acting relay for closing the said primary magnet circuit.

9, In a telephone system, a selector switch having directive primary and automatic sec ondary movements. primary and secondary motor magnets, a line relay having a pair of contacts closed when the relay is energized, a circuit for the primary magnet incontacts at thebeginning of the series and to open the same atthe end of the series,

10. In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a line relay having a pair of contacts closed when the relay is energized,

a normally open circuit for the primary magnet passing through said contacts, means for momentarily deenergizing the line relay a plurality of times, a slow acting relay maintained energized by the line relay during a series of deenergizations thereof. contacts on saidslow ac-ting relay for closing the said primary magnet circuit when the relay is energized. and a circuit for said secondary magnet closed by said slow acting relay when the relay is deenergized. A

11. .In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a line relay having a pair of contacts closed when the relay is energized, a circuit for the primary magnet in- .c I eluding said contacts and a second pair of. normally open contacts, means for causlng a series of deenergizations of the line relay, a slow acting "clay maintamed energized by the line relay during said series of deenergizations to close said secondpair of contacts at the beginning of the series andto open the same at the end of the series and a circuit for said secondary magnet closedby said slow acting relay when the same is deenergized. I

. 12. In a telephone system, a selectorswitch having primary and secondary movements, primary and secondary motor magnets, means for operating the primary magnet ot said switch to cause the primary movementthereof, a circuit for the secondary magnet, a low resistance stepping relay energized at the beginning of the primary movement to close a point in said circuit, means for completing said circuit at the end of the primary movement, a switching relay, a test circuit for intermittently actuating said stepping relay to operate the secondary magnet by means of the said circuit thereof, said test circuit excluding said switching relay, a circuit for energizing the switching relay in series with the said stepping relay at the end of the secondary movement, and contacts on said switching relay for opening the circuit of the said secondary magnet toprevent the operation thereof in case the said stepping relay is energized when connected in series with the switching relay. 7

13. In a telephone system, a trunking section comprising incoming and outgoing trunks, each trunk having two line conductors and-a release trunk conductor, a switch ing device for each incoming trunk comprising' a relay for each outgoing trunk, means means including a switching relay, a circuit completed over the release trunk conductor of an incoming trunk when sald trunking section is taken for use for energizing the 'particularrelay of the associated switching device which corresponds to an idle outgoing trunk, and means establishing a holding circuit for said last mentioned relay and the winding of the switching relay connectedin parallel.

14. In a telephone system, a trunk selecting switch having directive primary and automatic secondary movements, a plurality of trunking sections accessible thereto, each trunking section having a plurality of out going trunks, a switching device for each of said trunking sections comprising a relay for each omgoing trunk, and a' circuit completed when "the selecting switch selects a trunking section for energizing the particular relay of the associated switching device which corresponds to an idle outgoing trunk.

15. In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a line relay, a switching relay for disconnecting the line relay, circuits for said magnets controlled jointly by said relays, a trunking section accessible to said switch, said trunking section having a plurality of outgoing trunks, a relayfor each outgoing trunk, and circuit connections including the winding of one of sald last mentioned relays associated with an idle trunk and the winding of the switching relay, es tablished when the selector selects the trunk section. I

16. In a. telephone trunking section, in-

coming and outgoing trunk lines each having two line conductors and a release trunk conductor, a relay connecting the two trunks when it is operated, a circuit established over the release trunk conductor of the incoming trunk line when that trunk line is taken for use for temporarily operating the relay, and a circuit established over the release trunk conductor of the outgoing trunk line for maintaining said relay operated.

17. In a telephone trunking section, a plurality of incoming trunks, an outgoing trunk, a relay individual to each incoming trunk for connecting it to the outgoing trunk, each incoming trunk including a release conductor, means for energizing all the relays over any one of said last mentioned conductors, and means eflective upon the initial operation of the relay in the trunk containing the conductor over which the relays are en- 'for taking said trunk section for use, said ergized to open the circuit for the other re lays.

18. In a telephone trunking section, a plurality of incoming trunks, an outgoing trunk, a relay individual to each incoming trunk for connecting it to the outgoing trunk, each inconiing trunk including a re- .lease'conductor, means for energizing all the relays over any one of the release conductors, means controlled by each relay for preventing its full operation over the conductor of any trunk other than the trunk to Which it is individual, and means effective upon the initial operation of the relay in the trunk containing the release conductor over which the relays are energized to open the circuit of the othe relays.

19. In a telephone trunking section, plurality of outgoing trunks, a greater number of incoming trunks, a plurality of relays for connecting any incoming-trunk with any "idle outgoino' trunk, m ans dependent upon which outgoing trunks are busy to predetermine the next outgoing trunk to be taken for use, and switching means for changing the sequence with which the outgoing trunks are taken into use.

20. In a telephone trunking section, a plu- 'ality of outgoing trunks, a. greater number of incomin trunks a iluralit of relavs individual to each incoming trunk each for connecting the trunks to a different outgoing trunk, means effective when any incoming trunk is taken into use for operating the relay of that incoming trunk which corresponds to a preselected idle outgoing trunk to connect the two, and means controlled by said relay to preselect a. different idle outgoing trunk to be next taken into use, the

selection of the outgoingtrunk being the same regardless of which incoming trunks are taken into use.

In a telephone system, a directively operated switch having primary and secondary movement, said switch including a line relay having front and back contacts, a slow to release relay operated over a circuit including a front contact on the line relay, a second slow to release relay operated over a circuit including a back contact on the line relay and a front contact on the first sloW to release relay in series, and a motor magnet for giving the switch its primary movement, the circuit for the motor magnet being controlled ove a front contact on the line relay and a front contact on the second slow to release relay in series.

In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a line relay having front and back contacts, a slow to release relay operated over a circuit including a front contact on the line relay, a second slow to release relay operated over a circuit including a baclf contact on the line relay and a front contact on the first mentioned slow to release relay, the circuit for the primary motor magnet being controlled over a front contact on the second mentioned slow acting relay and a front contact on the line relay, and the circuit for the secondary niotornnagnet being controlled over a back contact on the second mentioned slow acting relay and a front contact on the line relay.

.23. In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a line relay having front and back contacts, a slow to release relay operated over a circuit including a front contact on the line relay, a second slow to release relay operated over a circuit including a back contact on the line relay and a front contact on the first mentioned slow to release relay, the circuit for the primary motor magnet being controlled over a front contact on the second mentioned slow acting relay and a front contact on the line relay, the circuit for the secondary motor magnetbeing controlled over a back contact on the second mentioned slow acting relay and a front contact on the line relay, and means efiective until the second slow to release relay operates to prevent the movement of the secondary magnet.

24. In a telephone system, a selector switch having directive primary and automatic secondary movements, primary and secondary motor magnets, a switching relay having. a back contact, a line relay having both back and front contacts, the circuit for both of said magnets including the back contact on the switching relay and a front contact on the line relay, and a slow acting relay having front and ba k contacts, the circuit for the primary magnet extending through a front contact on said slow acting relay and the circuit for the secondary magnet extending through a hack contact on said slow acting relay, and means for maintaining the slow acting relay operated only during the time that impulses are being transmitted to the line relay.

RODNEY G. RICHARDSON. 

